In the frame of GNSS signals, several systems use Direct Sequence Spread Spectrum (DSSS) and Binary Phase Shift Keying (BSPK) for modulating the signals. For instance BPSK modulation is used in the (NAVSTAR-) GPS (Global Positioning System) signals GPS L1-CA or GPS L5. BPSK has the advantage of being easily generated at the transmitter or receiver side. However, for a defined chip rate, a BPSK (modulated) signal is not as efficient in terms of code tracking performance and multipath robustness as other pulse shapes, for instance Binary Offset carrier (BOC) modulated signals. The main reason is that the pulse shapes of BOC modulated signals have a larger spectral bandwidth and are, therefore, more beneficial for tracking performances. In the signal terminology, this useful bandwidth is called the Gabor bandwidth, which is determined by the particular shape of the PSD (Power Spectral Density) function of the signal pulse shape.
New code discriminator techniques have been developed to improve the code tracking performances at receiver side of navigation signals using the BPSK pulse shape. As an example, two of these techniques are described in the publications “Theory and Performance of Narrow Correlator Spacing in a GPS Receiver,” Van D., Fenton, P., et al., Navigation: Journal of the Institute of Navigation, Vol. 39, No. 3, Fall 1992, and “Modified High Resolution Correlator Technique for Short-delayed Multipath Mitigation,” So H., Kim G., et al., Journal of Navigation 2009, Vol. 62, pp. 523-542.
Another way to improve code tracking in multipath environments at receiver side is shown in the publication “GPS Multipath Mitigation: How Good Can It Get with New Signals?,” Lawrence R. W., GPS World, June 2003, which describes an implementation of a multipath mitigation algorithm based on the statistical theory of maximum likelihood.
However, most of these techniques do not improve efficiently simultaneously the code tracking performance in a noisy environment and in a multipath environment, for a given transmitted signal pulse shape, like a BPSK.